I think Microsoft can still have great looking games, even better looking than PS5 since they have the power to do so. The difference (if noticeable) will be from the game design. Sony got all their first party studios working on PS5 since 2 years ago (IIRC), and something they do pretty well is taking advantage of their hardware.
Like Mike Cerny said, the SSD is not only for lower load times (or any), but it allows for completely different design philosophy. If that is something that can be conveyed since the beginning, and it's something that is actually noticeable, it will be very impressive.
Microsoft will make the games look great, but it will just be like a higher resolution, better textures, etc. from an Xbox One game. Sony on the other hand, COULD do something actually innovative.
I still think that Sony committing to the PS5 ( and a generational change overall) it's a smart move. They know that people move on regardless, because games start being developed for the newer console sooner or later. Also, they want people to move to the PS5 faster, so having games that they can only play on PS5, is what's going to entice people to do so.